1. Field of the Invention
The present invention relates to an image scanning system and a related method, and more particularly, to an image scanning system and a related method for calibrating sizes of scanned images.
2. Description of the Prior Art
Devices with a scan module, such as a multi-function printer (MFP), a facsimile (fax) machine, a photocopier, a printer or a scanner, usually utilize optical sensors or contact sensors to scan documents. For a device utilizing optical sensors, there is an optical module including a tube, a reflecting mirror, a lens and a charged coupled device (CCD). With precise calculation and design, light illuminated from the tube to the image will reflect to the reflecting mirror and then be reflected by the reflecting mirror to pass through the lens, to be received and sensed by the CCD to generate data of the image. It is obvious that the accuracy of the image and the preciseness of the device are closely linked.
Usually, there are several different resolutions provided by a scanning device. The higher the selected resolution is, the more pixels present in the original. Therefore the quantities of scanned pixels of the same image under different resolutions are different. Besides, limited by the characteristics of the sensors and the structure of the scan module, some image processing such as shading correction and Gamma correction of the scanned data is necessary for reducing the distortion of the image data.
For producing a copy identical to the original by a printer or a photocopier, it is very important to scan the image correctly. At present, calibrations of scan modules are performed during the process of manufacturing. The correctness of scanning is limited by the device and is determined when leaving the factory. However, due to inevitable errors in the process, transport conditions, and deviation of mechanisms caused by the improper use, the accuracy of the device changes after it leaves the factory and the sizes of the scanned image and the original one differ from each other. In this way, the image printed by the printer or the photocopier is distorted, and there is inaccuracy in the further data processing. For example, when a scanner scans an image under 600 dpi resolution, if the length of the image in the horizontal direction is 1 inch, the scanner should generate 600 pixels in the horizontal direction. However, when there is distortion, the scanner is not able to generate 600 pixels correctly. If the image is enlarged in the scanning, the scanner will read more than 600 pixels, such as 625 pixels. Without proper calibration, there will be an error in further data processing, printing, or image copying. For example, if the scanned image is printed out under 600 dpi resolution, the length of the image in the horizontal direction becomes
  1  ×      625    600  inches, which is different from the size of the original image.
There have been many approaches to try to solve distortions formed in the manufacturing process, that is, to solve distortions formed before the product leaves the factory. However, inaccuracy as a result of transportation conditions, and deviation of the scanner mechanism caused by the improper usage is not yet correctable.